DE2050154A1 - Corrosion-resistant inhomogeneous hard metal bodies and process for their production - Google Patents

Description

Fried, Krupp limited liability company in Essen

Corrosion-resistant, inhomogeneous hard metal bodies and Process for their manufacture.

It is known to produce hard metal bodies by sintering one of them Carbides, especially tungsten carbide, and to a lesser extent, For example, up to 20% of a powder mixture consisting of a lower melting binder metal, e.g. cobalt, nickel, iron. Such hard metal bodies are found in technology in particular for metal-cutting and non-cutting forming as well as large-scale use as wear parts. However, their use is in such There are limits to cases in which, for example in the chemical industry for pumps, plungers or shaft bearings, chemical substances come into effect. This disadvantage is essentially due to

the
that ensure the / required toughness of the hard metal body

Binder metals in contrast to the carbides against the attack of chemical Fabrics are not sufficiently resistant.

The object of the present invention is to create hard metal 11 bodies, which, in contrast to the previously known shaped bodies, withstand the attack of chemical substances to a sufficient degree, that is to say they are corrosion-resistant are. This object is achieved according to the invention by inhomogeneous hard metal bodies, the core of which is made of a sintered carbide and binder metal-containing mass and its surface zone Carbides and carbon or corrosion-resistant plastic exists, so does not contain any binding metal.

The invention also relates to a method for production such corrosion-resistant hard metal body. This method

EV 139/69

Bk / Wg. _ ι _

209817/0389

GiNAl- ;; ·; £ ■ · ECTED

consists in that in the usual way by sintering one out hard carbides and lower melting binding metal compound powder mixture manufactured hard metal bodies on the Binding metal is removed from the surface, for example by the action of an acid, e.g. hydrochloric acid, and the result is that formed pores are filled with carbon or corrosion-resistant plastic. That way the tenacious binder metal-containing compounds that ensure good mechanical properties The core of the hard metal body is retained, while the surface zone, which is free of binding metal, consists of substances that are corrosive to attack Substances offer sufficient resistance. The strength of the surface zone free of binding metal depends on the time of action of the the binder metal removing agent; it can be, for example, about 0.1 to 4 mm.

The introduction of the corrosion-resistant plastic into the Pores of the surface zones can be carried out in such a way that the monomer of the plastic with a catalyst in the pores are embedded and then polymerized to plastic by heating. However, aqueous plastics can also be used dispersions are introduced into the pores, the water then evaporating and the remaining plastic through Heating is sintered.

The incorporation of carbon in the pores can be experienced by carbon-containing carbon in a process carried out with the exclusion of air Plastics can be achieved that have previously been introduced into the pores.

The introduction of the plastic monomer or the plastic dispersion into the pores can be accomplished in this way be that the after the removal of the binder metal in the

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Outer layers of porous hard metal bodies degassed in a vacuum at elevated temperature and after cooling to room temperature still in a vacuum with the liquid monomers provided with a catalyst or with the plastic dispersion will. Normal pressure is then set and then for better storage of the liquid in the pores in the autoclave a nitrogen pressure applied so that a complete filling of the pores is guaranteed. It is known as To use a catalyst in the polymerization of furfuryl alcohol mineral acids, e.g. hydrofluoric acid. It has, however shown that it is more advantageous within the scope of the present invention. Dicarboxylic acids, e.g. oxalic acid, as a catalyst for To bring application, because then the polymerization proceeds more slowly and thus enough time for the complete filling of the There are pores of the hard metal body with the monomers,

The process on which the invention is based is explained in more detail below with the aid of examples.

example 1

A cemented hard metal body containing carbides and binding metals cylindrical shape (length 80 mm, diameter 10 mm) is treated with heated ÄWirtger hydrochloric acid for 24 hours.

Then the hard metal body is washed with hot water, until no more hydrochloric acid can be detected in the washing water, and dried with 96% ethanol. Then he becomes in

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Outgassed vacuum at 10 Torr and at a temperature of 400 C, after cooling, still under vacuum, covered with furfuryl alcohol, which contains 1 percent by weight of oxalic acid, broken to normal pressure and exposed to a nitrogen pressure of 50 atmospheres for 60 hours in the autoclave. That way Carbide bodies impregnated with furfuryl alcohol and catalyst in the surface zones are then blocked in a

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Coal bed excluding atmospheric oxygen slowly heated to 250 C within 5 hours, whereby under the action of the oxalic acid serving as a catalyst, the polymerization of furfuryl alcohol to form Furfuryl resin takes place

Example 2

One according to Example 1 to outgassing and then Treated hard metal bodies cool down while still under vacuum overlaid with a plastic dispersion consisting of 10 percent by weight polytetrafluoroethylene, the remainder being water, brought to normal pressure and then exposed to a nitrogen pressure of 50 atmospheres for 60 hours in an autoclave « After this treatment, those are in the surface zones dos Hartmeta 11 body contained I'oien with the plastic dispcHon filled out. The hard metal I Iköt per is then Dried for 2 hours at 110 C and then Heated for 4 hours at 360 to 400, which results in sintering of the plastic.

Example 3

A hard metal body produced according to Example 1 is shown in Embedded carbon powder and brought to the final temperature of 1000 C over a period of 8 hours, with the in the Furfuryl resin containing pores is cracked, leaving behind carbon. A metallographic micrograph shows that all contained in the surface zones of the hard metal body Pores are filled with carbon.

The hard metal body treated in this way is at 20 ° C. and for 3 days Was exposed to the attack of 20% hydrochloric acid for 4 hours at boiling point. Here, the hard metal body suffered no weight loss and there were no traces in the acid used

detectable of binding metal. _p ..,

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Claims (7)

5 2übü1b4 Claims O Corrosion-resistant inhomogeneous hard metal bodies, characterized in that the core consists of a sintered compound containing carbide and binding metal and the surface zones made of carbides and carbon or corrosion-resistant plastic. 2. Hard metal body according to claim 1, characterized in that that the thickness of the surface zones is about 0.1 to 4 mm. 3. Process for the production of hard metal bodies according to the Claims 1 or 2, characterized in that by Sintering of a hard metal body made of hard carbides and binding metal For example, the action of an acid on the surface removes binding metal and the resulting formation Pores are filled with carbon or corrosion-resistant plastic. 4. The method according to claim 3, characterized in that The monomers of a plastic are stored in the pores with a catalyst and then by heating to form the plastic is polymerized. 5. The method according to claim 4, characterized in that dicarboxylic acids, e.g. oxalic acid, are used as a catalyst. 6. The method according to claim 3, characterized in that aqueous plastic dispersions are introduced into the pores, then the water evaporates and the remaining plastic is sintered by heating, 2 0 U 8 I 7/0 3 8 9 7. The method according to claims 3 to 6 _t, characterized in that carbon-containing plastic introduced into the pores is subjected to a C rac kv experience for the purpose of producing carbon with the exclusion of air. -6 - 2098 1 7/0389